Electrolysis.



PATENTED JULY 23, 1907.4

G. RAMB-ALDINI. BLEGTROLYSIS. APPLIOATION FILED Dno.2.1904.

nl: Mouais Psrsns co., wlxsnmaran. u. f.

GIOVANNI RAMBALDINI, OF GROSSETO, ITALY.

ELECTROLYSIS.

Specification of Letters Patent.

Patented July 23, 1907.

*Original application led January 28, 1902, Serial No. 91,599. Divided and this application filed December 28, 1904.

v Serial No, 238,691.

To all whom it may concern:

Be it known that I, GIovANNr RAMBALDINI, a subject of the King of Italy, residing at Grosseto, Italy, have invented a new and useful Improvement in Electrolysis, of which the following is a specification.

My invention consistsof an improvement in electrolysis, the same being a division of an application filed by me January 28, 1902, Serial No. 91,599.

It frequently happens in the electro-chemical and electro-metallurgical industry that it is necessary to effect electrolysis while keeping the liquids of different natures which are in Contact with the two electrodes separate one from the other. This separation, as is well known, must not be complete; but, while avoiding the mixture of the salts dissolved, it must always permit of the conveyance of electric charges from one liquid to the other and vice versa, that is to say, the passage of the electric current from one electrode to the other through the liquid should not be interrupted. At first the problem was solved almost always by the employment of porous partitions; but such partitions have almost, invariably given bad results in practice, especially in installation of any size, owing to the number of elements. In addition to this, if the electrolytic process requires that only one of the two liquids shall play a direct part in this action, while the other liquid has onlya secondary action termed depolarization, and if it does not exert any action other than serving as a medium for conveying the ions produced by the decomposition of the first, as usually happens in cases where it is a question of separating from a mixture of different metallic salts one of these salts, the porous partition does not act and is ineffectual for the purpose for which the said separation is intended. It was therefore necessary to find a more certain and practical means, adapted to entirely replace the porous partition while at the same time obviating the grave defects of this latter; a means which would also insure the principle of independence in action of each of the two liquids in the transmission of the electric current.

The problem may thus be stated in the following terms. Maintain separated two different liquids without employing membranes or diaphragms of solid porous material, but retaining between them liberty of electrolytic transmission, in the sense of liquid velectric communication for the movements or exchange of the ions, 'and while permitting that by the electrolytic process these two liquids may become modified and act according to two laws, which, if need be, may be independent of and diverse from each other. ral that, for replacing the porous partition, separation owing to difference in the densities of the two liquids should have been first of all attempted. But the mere separation of the two liquids owing to the difference of It was natutheir specific weights, even when this is possible and convenient from certain lpoints of view, cannot fulfil the condition of preventing the. immediate contact of the two liquids. The principle of difference of density had therefore to be applied in conjunction with other expediente, with' the intervention of the principle of secondary actions. It is essential that the two solutions, having the most suitable densities, should be maintained separated by strong impermeable walls, and that their electric communication should be effected on the one hand by the electrodes and by the ordinary metallic circuit, and on the other by a liquid much lighter than the two solutions and situated above these latter.

Figure 1 is a diagrammatic view illustrating the invention. Fig. 2 is a similar view. Fig. 3 is a vertical cross section through a vessel showing its diaphragms, etc. Fig. 4 is a vertical longitudinal section through a form of apparatus embodying the invention. Fig. 5 is a vertical cross section of the same on the line 5-5 of Fig. 4.

A circuit arranged in accordance with these principles is diagrammatically represented in Fig. 1. Two electrodes metallically connected one with the other, the two liquids a and c being in contact with the electrodes, and between them the liquid conductor b, which in addition to the electric charges is able to convey the corresponding ions. The intermediate liquid conductor is the electrolyte properly so called E (Fig. 2); the two solutions in contact with the electrodes both serve in many instances as depolarizing agents (D being the positive depolarizer and D2 the negative depolarizer) for the two ions corresponding to the intermediate liquid, or only one if the anode is soluble. The useful work is then the effect of one or more secondary phenomena which may be produced as a result of these depolarizations. It will therefore be understood that the useful work, considered as a secondary phenomenon, may be varied in several ways by changing the depolarizing agents while keeping the third liquid invariable, especially if it is agreed to call the soluble anode the solid depolarizer.

In practice the arrangement may be that represented diagrammatically in Fig. 3. A vessel t of non-conducting material, or rendered non-conducting, is provided with a non-porous diaphragm t, also of insulating material which terminates somewhat below the edge which divides the vessel into two compartments u w in which, and to within a certain height from the top of the partition are the two depolarizingliquids, the positive in u and the negative'in w, separated one from the other. These liquids are both covered at y by a third solution which is much lighter and a conductor, which almost completely fills the vessel, extending much above the edge of the diaphragm. Slightly below the meniscus of separation, are arranged the two r electrodes Z Z, of any convenient form and nature, which are suspended by means of the metallic conductors m, m, which are insulated where they are immersed in the liquid and are connected externally to a source of electrical energy n.

Generally speaking it is advantageous to employ as third liquid a dilute solution of the acid which is combined with the salt which it is desired to decompose, in order to obtain the metal, or to separate from a mixture other salts having the same acid radical. Thus, for example, in the Siemens process for the electrolytic precipitation ofcopper from the mother waters containing this metal in the state of sulfate, the third liquid may be constituted by a dilute solution of sulfuric acid; in the Hoepfner process, where the copper is in the state of cuprous chlorid, the third liquid may be a dilute solution of hydrochloric acid; for the separation of sulfate of copper from the waters of cementation, dilute sulfuric acid may be used, and so forth. This point of view responds well to all the conditions of the electrolytic process, and is extremely useful from the industrial standpoint.

The industrial apparatus which I propose to employ for the practical application of my three-liquid method of electrolysis is diagrammatically represented in Fig. 4 in longitudinal section and in Fig. 5 cross section. In its most simple form it may be considered as the assemblage of three vats A. B. O. communicating one with the other by means of two series of lower tubes; the first series establishes communication between A and B and the second between B and C. As shown in the drawing, the tubes proceeding from A terminate in the middle vessel B in close proximity to its bottom, those proceeding from the vessel C enter the vessel B slightly below the surface of the lower liquid contained therein. In order to obtain the complete separation of these liquids the two lateral vats A, G are both divided into two longitudinal portions l, 2, entirely separate one from the other, while the middle vat B is divided into severalvtransverse compartments by diaphragms 4 which however only extend slightly above the outlet orifices from B to C and terminate well below the top. The tubular communications between the three vats are such that one of the longitudinal chambers of each of the vats A, C (l for example) is able to communicate with the series of uneven number of the compartments of the vat B, while the other chamber 2 is in communication with the series of even number.

For the sake of clearness and in order to show how this apparatus may be employed practically and the manner of its operation, I will now describe the particular case of the separation of sulfate of copper from the waters of cementation; but of course the manner of application does not vary in other cases where the system of electrolysis above referred to is suitable, so that the considerations which follow may be readily generalized. As is well known, the waters of cementation are amixture of sulfate of copper with other metallic sulfates, among which are generally found in great preponderance sulfates of iron. After any suitable and readily effected preparation which is capable of converting the ferric sulfate into ferrous sulfate,

these waters, at the maximum density compatible with the normal temperature for their treatment are caused to fill the cells of even number of the vat B, while the cells of uneven number are filled with a solution of sulfate of copper at 20 to 25 Baume. In both series of cells the solutions are caused to rise some centimeters higher than the right hand upper orifices and above these solutions water acidulated to 10 to 15 Baume with sulfuric acid is carefully poured almost up to the edge of the vat, in vsuch a manner as to establish a sharp division between this liquid and the two lower solutions. The compartments 1 of the two small lateral vats are filled simultaneously with a solution of sulfate of copper and the vats 2 with mother waters, that is to say with waters of cementation; in the condition of repose the free levels will arrange themselves at such heights that all the liquid columns reduced to the same specific weight establish equilibrium through the tubes. Beneath the menisci of division and some centimeters below it are horizontally arranged the copper or copper covered electrodes of suitable form suspended from above by the electric conductors which, as already stated, should be insulated where they are immersed in the liquid. These conductors are fixed to a horizontal transverse bar in any manner which will permit of metallic'communication between the vertical rods and the two longitudinal conductorsananged laterally at the top of the vat B; the bars of the cells of uneven number establish me'- tallic contact with the positive conductor, those of even number with the negative conductor only. The metallic circuit is closed upon an external source of energy and the current, on reaching the electrodes No. 1, is able to pass through the liquid to the electrodes No. 2 surmounting the partitions, and thence it is able to pass back to the metallic circuit. In this particular I case the electrolytic process is effected in the following mannerz-The electrolyte (sulfuric acid is decomposed into its two ions H2; S04: H2, proceeds to the negative pole and in presence of the sulfate of copper of the waters of cementation it again forms sulfuric acid and precipitates upon the cathode metallic copper.

(1) CuSO4+H2=H2SO4+Gu the sulphion SO4 proceeds to the positive pole; it cannot become xed upon the liquid in contact with the electrode, because the sulfate of copper is already a stable compound and it continues to the anode where with the metallic copper it forms a sulfate of copper.

where e isthe difference of potential at the electrodes,

There is r the resistance of the bath and i the intensity of the current. The useful work obtained is due to a secondary phenomenon because it is the effect of the depolarization at the anode, which, being soluble, acts as a depolarizer, and is in this case a liquid, that is to say, the solution of sulfate of copper formed in contact with the electrode. The depolarizer, that is to say, the soluble anode, is constantly regenerated at the cathode as a new effect of depolarization. In this arrangement the efficiency is the highest possible, that is to say, theoretically 100%, less the trifiing loss due to heat, because all the sulfate of copper which is formed at the positive pole remains there and may be collected integrally and the different velocities of the two ions SO4 and Cu, the transfer of which constitutes the phenomenon of the electrolysis, is the reason why the losses of concentration arising from the electrolysis at the anode and at the cathode are in the same respective ratio one with the other but inversely to these velocities, that is to say as 1 to 2. This consideration of the different velocity of transference of the different ions dissolved, applied to the electrolysis of the third liquid, has as a consequence that when an equivalent of copper precipitates at the cathode or dissolves at the anode, there are wanting at the anode 0.79 equivalents of sulfuric acid approximately, and at the cathode only 0.21. For this reason there remain finally in the mother waters of cementation only 0.79 equivalents of acid instead of the entire equivalent which is regenerated there in accordance with (l). This part of acid, which can no longer be employed for the electrolysis represents in this case a real consumption, and conjointly with that which passes `in the same mother waters by the effect of the diffusion from above and with that employed also in the form of water acid# ulated to 5 to 15%, for -correcting the diffusions of salts from below upwards in the third liquid, will constitute an expense with which the treatment must be charged. Experience however shows that this acid may be utilized for other operations of the hydrometallurgical process of which electrolysis is only one of the phases.

The addition of the acid which gradually decreases in the third liquid may be made partially in the solution of sulfate of copper during its circulation, and partly directly from above, suitable precautions being taken. The electrolytic process is in this particular caseV of a nature to oppose an obstacle to the diffusion through the menisci of division of the liquids by fixing towards the electrodes the respective depolarizing solutions. Experience shows also that a transfer of the unelectrolyzed salts takes place and that it is shown always in the -direction of the current, to which it is proportional, and finally which depends solely upon the ratio between the quantity of unelectrolyzed salt which is considered and the sum of this quantity and of those of all the other salts dissolved including that which is electrolyzed. This transfer of the unelectrolyzed salts, which is not prevented by the simultaneous presence of the acid of the same nature (it is facilitated even) acquires in this particular case, as in any other case of three-liquid electrolysis, considerable importance, because it serves to prevent at the negative pole diffusion upwards of all the salts dissolved in the corresponding solution which the object of the electrolytic process is to separate from the salt which takes an active part in the electrolysis, or which merely must not be allowed to pass into the third liquid and thence also in the other liquid to the positive pole and vice versa.

The apparatus is capable of continuous and industrial operation.

The necessity for renewing the two lower solutions which have already attained the greatest possible degree of modification due to the nature of the electrolytic process, is obvious, and since it is always advantageous to agitate as energetically as possible the liquids in contact .with the electrodes, this exchange should take place continuously and with a movement as energetic as is possible without disturbing the third liquid so as not to displace the menisci of separation of the liquids. Now the apparatus is constructed in such a manner as to permit of a sufficient continuous circulation of the lower liquids, while at the same time leaving the third liquid at rest.

lf, after having effected the charging as described with reference to the particular case above described and when all is in equilibrium, a fresh solution mixed with metallic sulfate is caused to enter the vat A, this solution can pass from A into the cells of even number of B and from these into 2 of the vat C without the upper liquid taking part in the movement; and if the compartment 2 of G has been provided with a distributer c and the admission to A has been suitably regulated, after a few moments a condition of hydrodynamic equilibrium is obtained such that as much mixed solu tion enters 2 vatAas leaves 2 vat C (circulating continuously through B) without displacing there the menisci of separation of even number. This depends upon the appropriate arrangement of the tubes and upon the difference in density of the lower liquids and of the third liquid. The conditions of separation between the liquid No. 2 and the liquid No. 1 are not thereby disturbed and this second liquid No. 1 will also remain perfectly tranquil.

When once the regimen of this first circulation, which 1 will call No. 2, has been established; that is to say when once it has been arranged that there enters 2 of the vat A a given quantity of liquid and that the same quantity leaves 2 of the vat C, the circulation No. l may be initiated (this solution being a solution of sulfate of copper in the present case) in the same manner, and if all has been well proportioned, the regimen will not vary for either of these two circulations while the supplies at the admission and at the outlet remain the same. Consequently the menisci of division in B will always retain their absolute positions. And in order to be the more certain that vall the menisci of uneven number shall be at the same level, and that those of even number may also be at the same level, it is only necessary to effect communication between the vertical tubes of uneven number at their lower portion, and those of the other series respectively; because they all establish, as has been stated, communication of the vat B with the two lateral vats. These lower communications, if they are effected by means of longitudinal tubes which may be opened at one end, will also serve for emptying the three vessels simultaneously when necessary. Finally, by means of suitable partitions arranged within the cells 3f B, the movement of the liquids may be regulated in such a manner that it corresponds more t the object for Which the circulation is intended. It is obvious that a series of these vessels may be arranged in the manner of a cascade, obtaining from all of them an operation which is absolutely relil able and constant, it, after having established a given regimen, care be taken to maintain constant the supply of liquid entering the first apparatus of the said series.v In this manner, and by suHiciently increasing the number of elements, it may be arranged that the liquid which enters the first leaves the latter only when it has attained such a degree of transformation that it is no longer adapted to be employed for the .eleclytic process, in the particular case under consideration, theA mother Waters of cementation may be caused to issue exhausted or almost completely exhausted of copper, While the solution oi sulfate oi copper at its issue Will have acquired the greatest degree oi density l compatible With its temperature and With the necessity of not forming crystals in contact With the electrodes.

At this point such a solution is able to pass to concen-` tration and crystallization in order to again enter the cycle o i operations sufficiently diluted.

Having thus described my invention, what I claim as new and desired to secure by Letters Patent, is.L

1. A process which consists in employingr an electrolyte of less specific gravity in contact with and above two other electrolytes serving as anolyte and catalyte each. of the above three electrolytes containing` the same anion, and maintaining the levels of Contact substantially equal during electrolysis, as described.

2. A process which consists in interposing an impervious partition between two electrolytes serving as anolyte and catalyte having the same anion, placing in contact with and above said electrolytes, a third electrolyte of less specific gravity, and having the same anion, maintaining the levels of contact substantially equal, and supplying fresh anolyte and catalyte as the same are depleted by electrolysis.

The hereiu described process of electrolysis which consists in separating two liquids by an impermeable partition and electrically `onlyconnecting a third liquid therewith, said third liquid being of lighter specic gravity and at all times remaining thus different from said two liquids and overlying the latter, placing a horizontally-disposed electrode in each of said two liquids, said third liquid being of such a composition that its electrolytic decomposition products are not able to disturb the desired electrolytic effects in the electrode chambers, andthereby rendering the formation of pure products possible with a continuous iiowing in and out of the electrode liquids.

ln testimony whereof I have hereunto set my hand in presence ot two subscribing Witnesses this 23rd day of November 1904.

GIOVANNI RAMBLDINI.

Witnesses:

B. CARLO SALVOTTI, M. DE DRAGO. 

